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LM5036EVM-294: LM5036 Evaluation board reset circuit

Aneesh TS
Expert 1735 points

Part Number: LM5036EVM-294

Hi,

Anybody can explain the working of the reset circuit in LM5036  Evaluation board?.

The circuit is marked in a red color in the attachment.

Regards

Aneesh

  • 0
    TI__Genius 13660 points
    Hi Aneesh,

    Thank you for your question, let me have a look at it.

    Regards,
    Teng
  • 0 in reply to Teng Feng
    Expert 1735 points
    Dear Teng,

    Any idea about my query?

    Regards
    Aneesh
  • 0 in reply to Aneesh TS
    TI__Genius 13660 points
    Hi Aneesh,

    The AUX PSU voltage level is used to communicate with the secondary to enable fully regulated pre-biased startup.
    Before the main PSU starts the Aux will regulate at 140% of its normal regulated level. VAUX2 is above the 9.1V Zener voltage, Q7A will be ON and hence Q7B will also be ON. In this state the the secondary reference voltage applied to the non-inverting input of the error amplifier (U4) will be pulled close to SGND.
    Once the main PSU SS exceeds 2V the Aux is changed to regulate at 100% of its normal regulation level. VAUX2 drops below the 9.1V Zener voltage Q7A will turn OFF and hence also Q7B will turn OFF. This releases the short across the secondary reference voltage and it starts to charge the soft-start capacitor (C21) via resistor R10 to give a soft-start ramp, at the reference input of the error amplifier. This ends when the voltage on C21 reaches the reference voltage set by U5.

    Regards,
    Teng
  • 0 in reply to Teng Feng
    Expert 1735 points
    Thank you Teng